1. Field of the Invention
The present invention relates generally to a control system for an automotive automatic power transmission for an automotive vehicle. More specifically, the invention relates to a shift control for selecting speed ratio according to driving condition of the vehicle, in which is introduced a technology of predicting demanded engine load.
2. Description of the Background Art
In the automatic transmission, kick-down operation for selecting lower speed ratio for better vehicular acceleration performance is selected in response to acceleration demand. One example of shifting pattern in kick-down been illustrated in RE4R01A type Automatic Power Transmission Service Manual (A261C07) issued by Nissan Motor Co., Ltd. In the practical kick-down control, down-shifting timing is detected by detecting increasing of throttle valve open angle across a down-shifting criterion which is set according to the shifting pattern, with a certain lag time after initiation of increasing of depression magnitude of an accelerator pedal. With a further delay time due to lag time of hydraulic system governing the transmission speed ratio, down-shifting is actually performed.
In the worst case, the lag time in actually performing kick-down operation lags approximately 1 sec. from initiation of entry of the acceleration demand. Since kick-down operation is required in response to acceleration demand, such substantial delay in response will clearly degrade vehicle drive feeling. Also due to substantial delay in response, vehicular acceleration performance can be significantly lowered.